Illuminated sign



May 20, 1947. w. M. POTTER 2,420,976

ILLUMINATED SIGN Filed July 3, 1944 INVENTORZ WENTWORTH M. POTTER,

H l S.ATTORNEY.

?atented May 20, 1947 ILLUMINATED SIGN Wentworth M. Potter, Lyndhurst, Ohio, assignor to General Electric Company, a corporation of New York Application July 3, 1944, Serial No. 543,323

6 Claims.

My invention relates to electric signs of the type comprising an illuminated background viewed through suitable openings in the face of the sign. The principal object of my invention is to provide an optical system fo such a sign whereby the sign is visible and legible from great distances with a minimum expenditure of electric power. Another object of my invention is to provide such a sign which is self-contained and requires a minimum of maintenance so that it may be located in isolated places remote from central station sources of electric power. Further objects and advantages of my invention will appear from the following detailed description of species thereof and from the appended claims.

In the drawing accompanying and forming part of this specification a sign embodying my invention is shown in which Fig. 1 is a perspective view of the sign and Fig. 2 is a sectional view of the optical system of the sign shown in Fig. 1 and taken alon a diagonal of the sign face.

Referring to Fig. 1 of the drawing the sign comprises a box I having a lens plate 2 constituting one of its sides, selected portions of which are visible through an opaque, perforated sheet 3 fOlll'liIlg the face of the sign. The perforations 4 in the sign face 3 may be selected to make up various indicia o legends for advertising or signalling purposes: the letter X shown in the drawing being the conventional indication or warning of a road crossing.

The lens plate 2 is of square shape and constitutes part of the optical system (Fig. 2 of the sign which system is the source of brightness for the sign pattern and is made up of a light source 5, a reflector 6 mounted in light receiving relation to the source and which directs the incident light toward the lens plate 2. The reflected light is indicated by lines I in the drawing. The lens plate 2 also receives light directly from the source 5 and retracts both the direct light (indicated by broken lines 8 in the drawing) and the reflected light I to produce a narrow, substantially collimated light beam which is visible from substantial distances in a direction substantially normal to the sign face even when the source 5 is an incandescent lamp of low power consumption, of the order of .08 watt, for example, and produces but /8 to A lumen The lamp filament and the focus of lens 2 are located at L in the drawing.

The reflector 6 presents a specular surface of ellipsoidal or modified ellipsoidal contour to the source 5 and is symmetrical with the major axis of its generating ellipse, the said major axis being in the axis A-B of the optical system. The source 5 is disposed in the axis of the system and is offset from the focus F of the reflector 6 in the direction of the conjugate focus of the reflector. Thus, as shown by the lines 1 in Fig. 2, the reflected light is directed across the axis A-B of the system in any cross-section including the axis A-B and toward the outer portions or areas of the lens plate 2 to substantially increase the illumination and the candlepower on said areas. This distribution of reflected light is desirable because it compensates for the reduction of apparent brightness of the outer areas near the edges of the lens plate 2, which is of Fresnel or stepped outline having light refracting, annular prisms. The reduction in apparent brightness at-said outer lens areas is due, in large part, to the non-luminous risers of the lens prisms which risers increase in projected area, as viewed normal to the lens plate, as their distance from the center of the lens plate 2 increases. Hence, a higher level of illumination is required on the outer areas of the lens 2 to attain, for distant viewing, a more nearly uniform distribution of apparent brightness over the area of the sign face. This ishighly effective in making the sign legible from substantial distances.

- The lens plate 2 is spaced sufficiently from the source 5 and the reflector 6 and is of such size with respect to said spacing that it intercepts or accepts the direct light (indicated by lines 8 in Fig. 2) and the reflected light 1 at angles suitable for refraction into a beam of substantially parallel rays as shown. Of course, some of the reflected light strikes the lens 2 at higher angles than those at which light can be refracted into a beam of parallel rays but I have demonstrated that sufficient reflected light is refracted by the lens 2 in a direction parallel to the optical axis AB of the system to give the desired uniformity of brightness for the sign pattern constituted by the perforations in the sheet or sign face 3, when viewed normal to the sign face, or at small angles to the normal.

In forming indicia of the kind comprising strokes extending radially outward from the center of the lens plate 2, such as the X shown in Fig. 1, or the letter Y, I prefer to make the strokes of increasing width as the outer areas of the lens plate 2 are approached, the increase in width being approximately in the ratio of 10 to 1. For

other formsof indici'a having non-radial strokes, the width at. selected parts may, on the same basis, be made substantially proportionate to their distance from the center of the lens; in the case of circular indicia concentric with the center of the lens, constant width of stroke is indicated. The variations in width of stroke just described enhance the legibility of th sign as the larger area of the stroke extremity tends to compensate for residual variations in brightness and the increased width of this portion of the stroke tends to counteract or to overcome the optical illusion of fading out of the stroke extremitiespresent when strokes of rectangular shape are utilized. The stroke widths employed are relatively small.- particularly near the lens center, in order best to compensate for the apparent swelling effect of irradiation of a relatively bright area in high contrast with its surrounding areas" and seen in a relatively dark environment. The sheet 3 is preferably opaque at its center portion opposite the lens center, as shown in the drawing, to eliminate the highest brightness part of the lens and to facilitate making the stencil.

p I have demonstrated that a sign comprising an incandescent lamp having a powerconsumption of appimxiniat'eiy watt and a light output oi theorder'of to 7 l-uinen; an ellipsoidal, speeu Iar reflector having a major xi's of s inches and a minor axis of 3 ,5 inche melanin filament disposed or of "aninch fr no the reiiect'or focus inthe direction of the conjugate focus and with the outer rim or edge or the reflector a plane is? inches from the lamp n an approximately l2 inch square Velvet er-cues Holop-hane Controilens No. 755V. F; as shownin Fig; 2 with tliepri'sms outward and with the back face of the lens space-d approximately 6 inches fr m the lamp filament, and a cutout or stencil type letter, such as that shown in Fig, 1, which isil inches high and 11 inches wide is legible from a distance as great as #50 feet and visible iror'rr auist'an'oe of 2500- ft. leglpility distance of approximately 68 feet per inch; of letter height is extremely high in comparison with that round for typical lu inous sign letters and con tructrons, even when these are viewed in a brighter and more favorable" environment.

,The power source for the lamp 5 is preferably a: cont'erltlonal cell or the size and type used for ringing dour-hells and the use and is mounted in the box I. The box {is substantially light tight except fertile side constituted; by the lens plate 2 The-lamps is supported in the socket 9: which may be secured to a removable panel in the back of the box"? and connected across the terminals of the cell. frhe reflector 6 is frictionail or otherwise fitted to andthus supported by the socket s so that the lamp 5, the socket 9 and the reflector 6' may be removed as a unit tor cleaning; repairing and replacement. The sheet 3' and the lens late 2 are held on the box I by afrarne Hi bolted to the box I. The sheet 3 may beremoved' and another sheet having diiferent cut out letter may be substituted therefor by removing the frame.

The iilun'iin'ated sign described above (or its variations) is useful along a wayside or railway rig'lit-of-tvay in dark surroundings for such puras such signs are now used,- or as markers or warning-signs along highways, or in any locations where view occurs only" within specified limited angles near the normal to the sign face, or where ltn iay be desirable, for other reasons, to reduce greatly visibilityin other directions. The electric ceilfurnishes sufiicient electrical enorgy and the power consumption of the lamp is so low that thela np will operate continuously on the cell for a prolonged period. Thus, it is not necessary to provide an electric switch for com necting and disconnecting the lamp and the cell and frequent replacement of the cell is not necessary. The sign, being self-contained, may be located in places remote from central station power lines and frequent visits for replacement of the cell or the lamp are not necessary. The selfcontained feature of the sign may be dispensed with and suitable means provided for connecting the lamp to a; central station power source. A more powerful lamp may then be preferred to produce higher brightness for use in lighter surrcundings.

A double convex lens may be used in place of lens 2; a ribbed or fluted light transmitting member may be placed over the outer surface of lens 2 to spread the beam and thus increase the angle ofvieu in which the sign may be seen, and colored screens may be used over the face of the sign, when desired.

What I claim as new and desire to secure by Letters Patent oil the United States is:

1.. optical system comprising a light concentrating' lens which refracts light from its focal point into parallel rays and. the apparent brightmess of which decreases outwardly from its center under uniform illumination, a light source at the lens focal point and an. ellipsoidal reflector about said source, said reflector being symmetrical. with its major axis, said light source being adjacent but oiiset from one focus of said reflector so that the reflected light. impinges on said lens at angles suitable for refraction into parallel rays and the illumination by reflected light on said lens increases outwardly from the center of the lens to increase the apparent brightness of the outer areas of said lens.

2. Arr optical system comprising a light con.- centrating lens which retracts light from its focal point; into parallel rays arid the apparent brightness of. which: decreases outwardly from its center under uniform illumination, a light source at the lens focal point and an ellipsoidal reflector about said source, said. reflector being symmetriwitlo its major axis, said light source being adjacent but 'ofiset from one focus of said reflec tor in the direction of its conjugate focus so that the reflected light impinges on said lens at angles suitable for refractionintoparallel rays and the illumination by reflected light on said lens increases outwardly from the center of the. lens to increase the apparent brightness of the outer areas of said lens.

3. An optical system comprising a light concentrating lens which retracts light from its focal point into parallel rays and the apparent brightness of which decreases outwardly from its center under uniform illumination, a light source at the lens focal point and an ellipsoidal reflector about said source, said reflector being symmetrical with its major axis and having an open mouth in a plane intersecting its axis between its foci, said light source being adjacent but offset from one focus of said reflector so that the refieeted light impinges on said lens at angles suitable for refraction into arallel rays and the illamination by reflected light on said lens increases outwardly from the center of the lens to increase the apparent brightness of the outer areas of said lens.

4. An optical system comprising a light concentrating lens which retracts light from its focal point into parallel rays and which has light refracting annular prisms the risers of which increase in rojected area as viewed normal to the lens as their distance from the center of the lens increases so that the apparent brightness of the lens under uniform illumination decreases outwardly from its center, a light source at the lens focal point and an ellipsoidal reflector about said source, said reflector being symmetrical with its major axis, said light source being adjacent but offset from one focus of said reflector so that the reflected light impinges on said lens at angles suitable for refraction into parallel rays and the illumination by reflected light on said lens increases outwardly from the center of the lens to increase the apparent brightness of the outer areas of said lens.

5. An illuminated sign comprising a stencil type letter and a source of brightness for said letter, said source consisting of an optical system comprising a light concentrating lens which refracts light from its focal point into parallel rays and the apparent brightness of which decreases outwardly from its center under uniform illumination, a light source at the lens focal point and an ellipsoidal reflector about said source, said reflector being symmetrical with its major axis, said light source being adjacent but offset from one focus of said reflector so that the reflected light impinges on said lens at angles suitable for refraction into parallel rays and the illumination by reflected light on said lens increases outward-t 1y from the center of the lens to increase the apparent brightness of the outer areas of said lens, said letter covering said lens except for the lens portions visible through the perforations in said letter.

6. An illuminated sign comprising a. stencil type letter and a source of brightness for said letter, said source consisting of an optical system comprising a light concentrating lens which 6 refracts light from its focal point into parallel rays and the apparent brightness of which decreases outwardly from its center under uniform illumination, alight source at the lens focal point and an ellipsoidal reflector about said source, said reflector being symmetrical with its major axis, said light source being adjacent but offset from one focus of said reflector so that the reflected light impinges on said lens at angles suitable for refraction into parallel rays and the illumination by reflected light on said lens increases outwardly from the center of the lens to increase the apparent brightness of the outer areas of said lens, said letter covering said lens except for the lens portion visible through the perforations in said letter and having strokes radiating and increasing in width from its center.

WENTWO'RTH M. POTTER.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 2,293,014 Clarkson Aug. 11,1942 1,746,852 Champeau Feb. 11, 1930 736,722 Hall Aug. 18, 1903 2,074,249 Bloh Mar. 16. 1937 1,284,016 Wise Nov. 5, 1918 FOREIGN PATENTS Number Country Date 336,495 France 1904 26,238 Great Britain Dec. 4, 1908 

